A surface treatment method of coating a chromate film is generally used to provide corrosion resistance and coating adherence to a zinc plating steel sheet and zinc-based alloy plating steel sheet, an aluminum plating steel sheet, aluminum-based alloy plating steel sheet, cold-rolled steel sheet and hot-rolled steel sheet, which are used as materials for automobiles, electronic appliances and construction. However, according to the necessity of several countermeasures for a working environment and drainage treatment due to toxicity of hexavalent chromium, a chromium-free surface treated steel sheet which can meet various demand characteristics including corrosion resistance, alkali resistance and conductivity has been developed.
However, a conventional surface-treated steel sheet to which organic or combined organic-inorganic coating is applied has problems of discoloration and degradation in physical properties due to deterioration of a resin component as thermal stability of a coating component such as an organic material in a PDP panel is degraded during a long-term use at a high temperature of 200 to 250° C. or more.
To solve these problems of the surface-treated steel sheet, a coating steel sheet using a silicon-or fluorine-based resin having excellent thermal resistance has been used in the art. However, since the coating steel sheet is generally coated to 20 to 30 μm on an under coat having a thickness of approximately 5 μm so as to ensure durability, it cannot ensure electric conductivity, and is expensive. Therefore, the coating steel sheet has been used only for exterior materials for decoration of electronic appliances. As a surface-treated steel sheet for interior materials of an electronic appliance, an anti-fingerprint steel sheet having a coating thickness of approximately 1 to 2 μm on a zinc plating steel sheet has been widely used.
As shown in FIG. 1, such an anti-fingerprint steel sheet is generally formed to have a zinc plating layer on a top surface of the steel sheet and a resin layer including metal powder and/or a metal salt having conductivity on the zinc plating layer so as to provide conductivity in addition to corrosion resistance and/or alkali resistance.
Here, as the metal powder and/or metal salt used to provide conductivity to the resin layer, generally, zinc oxide is used in some cases, and to achieve 100% conductivity, the zinc oxide should generally be included in an amount of approximately 3 parts by weight or more based on a solid content of a conductive resin composition to form a resin layer.
Meanwhile, while materials known so far as a crystalline body of carbon are only graphite and diamond, in 1985, Kroto of Sussex University in the UK and Smalley of Rice University in the US found the presence of a fullerene referred to as a third carbon allotrope from an experiment of vaporizing a graphite using a laser beam, and in 1990, Kratschmer of Germany and Huffman of the University of Arizona succeeded in mass production of fullerenes using an arc discharge method instead of a laser beam, which served as a momentum for the active research of carbon materials. The most important result obtained from such research is discovery of a carbon nanotube.
A carbon nanotube is a tube-shaped material formed in such a manner that carbon atoms bind to one another carbon in a hexagonal honeycombed pattern, and a diameter of the tube is ultimately small on a nanometer (1/109 meter) level.
A carbon nanotube exhibits characteristics of a conductor or semiconductor according to a degree of a twisted structure and has a quasi-one-dimensional structure, unlike graphite and diamond respectively having characteristics of a conductor and a nonconductor. The carbon nanotube is not only a nano-structure having an unusual quantum effect, but also has characteristics of a quantum wire through which electric current theoretically flows at an ultra-high speed at room temperature with no resistance. In addition, the carbon nanotube has an electric resistance lower than graphite at room temperature, and is at least 100 times stronger than steel, very lightweight and chemically stable. The carbon nanotube increases in a magnetic property as a temperature lowers, which indicates that the carbon nanotube is diamagnetic.
However, graphene, which has an excellent conductivity at least 50% higher than that of the carbon nanotube, has also been discovered. Graphene has a thickness of one atom and is a good conductor having excellent electric performance. In graphene, electrons move as if they do not have a rest mass and have an unusual type of quantum hall effect.